Laser system including optical amplification subsystem providing an amplified laser output

ABSTRACT

A laser system including a seed laser and an optical amplification subsystem, receiving an output of the seed laser and providing an amplified laser output, the optical amplification subsystem including a first plurality of amplifier assemblies, each of the first plurality of amplifier assemblies including a second plurality of optical amplifiers, and phase control circuitry including phase modulating functionality associated with each of the first plurality of amplifier assemblies.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 13/701,045, filed Jan. 3, 2013, entitled COHERENTOPTICAL AMPLIFIER, the disclosure of which is hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to laser systems generally.

BACKGROUND OF THE INVENTION

The following publications are believed to represent the current stateof the art:

U.S. Pat. Nos. 6,400,871; 6,233,085; 5,896,219; 4,648,092; 6,882,781;5,946,130; 6,580,534; 5,737,459; 6,717,719; 7,336,363; 4,860,279;5,023,882; 7,088,743; 6,404,784; 6,144,677; 6,366,356; 6,678,294;6,480,327; 4,757,268; 5,121,400; 4,761,059; 4,833,683; 4,979,804;5,233,673; 6,200,309; 4,649,351; 5,661,747; 3,590,248; 7,239,777;6,385,288; 4,794,345; 5,835,261; 5,539,571; 7,027,475; 7,187,492;7,233,433; 7,058,098; 6,813,069 and 5,694,408;

U.S. Patent Publication 2006/0239312; and

“One Dimension Scaling of 100 Ridge Waveguide Amplifiers”, K. H. No etal, IEEE Photonics Technology Letters, Vol. 6, No. 9, pp 1062-66.

SUMMARY OF THE INVENTION

The present invention seeks to provide improved laser systems.

There is thus provided in accordance with a preferred embodiment of thepresent invention a laser system including a seed laser, an opticalamplification subsystem, receiving an output of the seed laser andproviding an amplified laser output, the optical amplification subsystemincluding a first plurality of amplifier assemblies, each of the firstplurality of amplifier assemblies including a second plurality ofoptical amplifiers and phase control circuitry including phasemodulating functionality associated with each of the first plurality ofamplifier assemblies.

There is also provided in accordance with another preferred embodimentof the present invention a laser system including a seed laser and anoptical amplification system, receiving an output of the seed laser andproviding an amplified laser output, the optical amplification systemincluding a first plurality of amplifier assemblies and first phasecontrol circuitry including phase modulating functionality associatedwith each of the first plurality of amplifier assemblies, each of thefirst plurality of amplifier assemblies including a second plurality ofoptical amplifiers and second phase control circuitry including phasemodulating functionality associated with each of the second plurality ofoptical amplifiers, the second phase control circuitry including a totaloutput intensity sensor which measures the total output intensity of thesecond plurality of optical amplifiers and phase control logic circuitrywhich receives an output from the total output intensity sensor andvaries the phase relationships of individual ones of the secondplurality of optical amplifiers in order to maximize the total outputintensity of the laser system as sensed by the total output intensitysensor.

Preferably, the first phase control circuitry operates independently ofthe second phase control circuitry. Additionally or alternatively, thesecond phase control circuitry of each one of the first plurality ofamplifier assemblies operates independently of the second phase controlcircuitry of each other of the first plurality of amplifier assemblies.

In accordance with a preferred embodiment of the present invention thephase control logic circuitry ascertains the current level supplied toeach of the second plurality of optical amplifiers which produces themaximum total output intensity of the laser system. Alternatively oradditionally, the phase control logic circuitry governs the phase of anexternal phase modulator associated with each of the second plurality ofoptical amplifiers which produces the maximum total output intensity ofthe laser system. Additionally or alternatively, the phase control logiccircuitry sequentially varies the current supplied to each of the secondplurality of optical amplifiers and selects the current level suppliedto each of the second plurality of optical amplifiers to be the currentwhich produces the maximum total output intensity of the laser system.

In accordance with a preferred embodiment of the present invention thephase control logic circuitry sequentially varies the phase of anexternal phase modulator associated with each of the second plurality ofoptical amplifiers and selects the phase of an external phase modulatorassociated with each of the second plurality of optical amplifiers to bethe phase which produces the maximum total output intensity of the lasersystem.

Preferably, the phase control logic circuitry sequentially varies thephase of each of the second plurality of optical amplifiers and selectsthe phase of each of the second plurality of optical amplifiers to bethe phase which produces the maximum total output intensity of the lasersystem. Additionally, multiple different ones of the second plurality ofoptical amplifiers are simultaneously supplied with current at differentlevels.

Preferably, the laser system also includes a coherent free-space farfield combiner receiving outputs from at least one of the first andsecond pluralities of optical amplifiers and directing the outputs to asingle mode optical fiber.

In accordance with a preferred embodiment of the present invention thelaser system also includes a coherent free-space far field combinerreceiving outputs having a first numerical aperture from at least one ofthe first and second pluralities of optical amplifiers and directing theoutputs to an optical fiber having a second numerical aperture similarto the first numerical aperture.

Preferably, the laser system also includes a coherent free-space farfield combiner receiving outputs from at least one of the first andsecond pluralities of optical amplifiers and coherently combining theoutputs into a single beam having an at least nearly Gaussian profile.Additionally, brightness of the single beam is substantially higher thanthe brightness of a corresponding non-coherently combined beam.

There is further provided in accordance with yet another preferredembodiment of the present invention a laser system including a seedlaser and an optical amplification subsystem, receiving an output of theseed laser and providing an amplified laser output, the opticalamplification subsystem including a plurality of optical amplifiers andphase control circuitry sequentially varying the phase of each of theplurality of optical amplifiers and selecting the phase of each of theplurality of optical amplifiers to be the phase which produces themaximum total output intensity of the laser system.

Preferably, the phase control circuitry ascertains the current levelsupplied to each of the plurality of optical amplifiers which producesthe maximum total output intensity of the laser system. Additionally oralternatively, the laser system also includes a coherent free-space farfield combiner receiving outputs from the plurality of opticalamplifiers and directing the outputs to a single mode optical fiber.

In accordance with a preferred embodiment of the present invention, thelaser system also includes a coherent free-space far field combinerreceiving outputs having a first numerical aperture from the pluralityof optical amplifiers and directing the outputs to an optical fiberhaving a second numerical aperture similar to the first numericalaperture.

Preferably, the laser system also includes a coherent free-space farfield combiner receiving outputs from the plurality of opticalamplifiers and coherently combining the outputs into a single beamhaving an at least nearly Gaussian profile. Additionally, brightness ofthe single beam is substantially higher than the brightness of acorresponding non-coherently combined beam.

There is even further provided in accordance with still anotherpreferred embodiment of the present invention a laser system including aseed laser and an optical amplification system, receiving an output ofthe seed laser and providing an amplified laser output, the opticalamplification system including a plurality of optical amplifiers, anoptical pathway directing an output from the seed laser to the firstplurality of optical amplifiers and a coherent free-space far fieldcombiner receiving outputs from the plurality of optical amplifiers anddirecting the outputs to a single mode optical fiber.

There is still further provided in accordance with yet another preferredembodiment of the present invention a laser system including a seedlaser and an optical amplification system, receiving an output of theseed laser and providing an amplified laser output, the opticalamplification system including a plurality of optical amplifiers, anoptical pathway directing an output from the seed laser to the pluralityof optical amplifiers and a coherent free-space fax field combinerreceiving outputs having a first numerical aperture from the pluralityof optical amplifiers and directing the outputs to an optical fiberhaving a numerical aperture similar to the first numerical aperture.

There is yet further provided in accordance with another preferredembodiment of the present invention a laser system including a seedlaser and an optical amplification system, receiving an output of theseed laser and providing an amplified laser output, the opticalamplification system including a plurality of optical amplifiers, anoptical pathway directing an output from the seed laser to the pluralityof optical amplifiers and a coherent free-space far field combinerreceiving outputs from the plurality of optical amplifiers and combiningthe outputs into a single beam having an at least nearly Gaussianprofile.

Preferably, brightness of the single beam is substantially higher thanthe brightness of a corresponding non-coherently combined beam.

There is also provided in accordance with still another preferredembodiment of the present invention a method of independentlycontrolling the phase and output intensity of an optical amplifierincluding first and second gain sections, a first electrode associatedwith the first gain section and a second electrode associated with thesecond gain section, the method including changing the phase of theoptical amplifier independently of the output intensity of the opticalamplifier by varying current supplied via the first and secondelectrodes in a first manner and changing the output intensity of theoptical amplifier independently of the phase of the optical amplifier byvarying current supplied via the first and second electrodes in a secondmanner, different from the first manner.

Preferably, varying current supplied via the first and second electrodesin the first manner includes increasing the current supplied to thefirst electrode and decreasing the current supplied to the secondelectrode, such that the output intensity of the optical amplifier isunchanged.

In accordance with a preferred embodiment of the present inventionvarying current supplied via the first and second electrodes in thesecond manner includes changing the current supplied to the first andsecond electrodes by different amounts such that the phase of theoptical amplifier is unchanged.

There is also provided in accordance with still another preferredembodiment of the present invention a method of independentlycontrolling the phase and output intensity of an optical amplifierincluding the use of an external phase modulator associated with each ofthe optical amplifiers. A suitable external phase modulator may be aLiNbO₃ modulator, such as a LN65S-SC-10 GHz Phase Modulator,commercially available from Thorlabs Inc. of Newton, N.J. Alternatively,phase modulators which are operative by varying the temperature of eachoptical amplifier, by mechanically changing the length of the opticalpath for each optical amplifier or by employing any other standard phasemodulation method may be used.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIG. 1 is a simplified illustration of a laser system constructed andoperative in accordance with a preferred embodiment of the presentinvention;

FIG. 2 is a simplified diagram illustrating total output intensity basedphase modulation;

FIG. 3 is a simplified flow diagram illustrating the operation of thetotal output intensity based phase modulation of FIG. 2;

FIG. 4A is a simplified illustration of an optical coherent combinerconstructed and operative in accordance with a preferred embodiment ofthe present invention, useful in the laser system of FIGS. 1-3;

FIG. 4B is a simplified illustration of an optical coherent combinerconstructed and operative in accordance with another preferredembodiment of the present invention, useful in the laser system of FIGS.1-3;

FIG. 5 is a simplified illustration of a laser system constructed andoperative in accordance with another preferred embodiment of the presentinvention.

FIG. 6A is a simplified illustration of an optical amplification andbeam combining sub-subsystem constructed and operative in accordancewith a preferred embodiment of the present invention, useful in thelaser system of FIG. 5;

FIG. 6B is a simplified illustration of an optical amplification andbeam combining sub-subsystem constructed and operative in accordancewith another preferred embodiment of the present invention, useful inthe laser system of FIG. 5;

FIG. 7 is a simplified illustration of a laser system constructed andoperative in accordance with another preferred embodiment of the presentinvention;

FIG. 8 is a simplified illustration of a laser system constructed andoperative in accordance with yet another preferred embodiment of thepresent invention;

FIG. 9 is a simplified illustration of a laser system constructed andoperative in accordance with still another preferred embodiment of thepresent invention; and

FIG. 10 is a simplified illustration of a laser system constructed andoperative in accordance with a further preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to FIG. 1, which is a simplified illustration of alaser system constructed and operative in accordance with a preferredembodiment of the present invention.

As seen in FIG. 1, there is provided a laser system including a seedlaser 100, typically a 50 MW laser, such as a LU0976M150-1306E10Acommercially available from Lumics GmbH of Berlin, Germany. The outputof the seed laser 100 is amplified by an optical amplifier 102,preferably a tapered optical amplifier, such as a .BTA_976_2000_DHP fromM2K Laser GmbH of Freiburg, Germany.

A current is supplied to an electrode of the optical amplifier. It isknown that changes in the current level typically change both the phaseand the intensity of the optical output of the amplifier.

It is a particular feature of an embodiment of the present inventionthat control of the currents to the ridge and taper electrodes of atapered optical amplifier can vary the phase of its output withoutvarying its output intensity.

This may be appreciated from the following discussion:

The current at each of the ridge and taper electrodes affects bothintensity and phase of the light emitted from the tapered opticalamplifier in accordance with the following known relationship:Θ_(R) =I _(R) ×A _(ΘR)Θ_(T) =I _(T) ×A _(ΘT)P _(R) =I _(R) ×A _(PR)P _(T) =I _(T) ×A _(PT)

The total intensity and phase herefore given by:Θ=I _(R) ×A _(ΘR) +I _(T) ×A _(ΘT)P=I _(R) ×A _(PR) +I _(T) ×A _(PT)

It has been found by the present inventor that it is possible to find aset of values for the ridge electrode current and taper electrodecurrent which allows variation of the phase of the output of a taperedoptical amplifier without changing the intensity of the output.

Alternatively, modulation of the relative phases of the opticalamplifiers may be realized by the use of external phase modulatorsassociated with each of the optical amplifiers. Suitable external phasemodulators may include an external phase modulator such as a LN65S-SC-10GHz Phase Modulator available from Thorlabs Inc. of Newton, N.J.Alternatively phase modulators which are operative by varying thetemperature of the optical amplifier, by mechanically changing thelength of the optical path for each optical amplifier or by employingany other standard phase modulation method may be used.

The output of optical amplifier 102 is preferably coupled via a network104 of optical fibers to an optical amplification subsystem 106,providing an amplified laser output. Preferably network 104 comprisespolarization maintaining single mode fibers, such as PM780-HP fibersavailable from Thorlabs Inc. of Newton, N.J., which are joined viasuitable beam splitters.

In a preferred embodiment of the invention, illustrated in FIG. 1,network 104 employs a 1×4 beam splitter 108, such as aPMC-1×N-3-4-2-2-2-0-0 from Micro Optics Inc. of Hackettstown, N.J.,which receives the output of optical amplifier 102 and directs it tofour optical amplifiers 110, arranged in parallel. The outputs of eachof the four optical amplifiers 110 are each directed to a 1×8 beamsplitter 112, such as a PMC-1×N-3-8-2-2-2-0-0 from Micro Optics Inc.

In accordance with a preferred embodiment of the present invention, thelevel of amplification provided by each of the optical amplifiersemployed in the laser system is significantly below the maximum ratedamplification of the amplifiers and is selected to maximize outputcoherence. More specifically, the level of amplification is selected tolimit the amount of phase distortion and wavelength broadening as wellas to limit noise and non-linear effects produced by the amplifier. Thelevel of amplification is also selected to limit the amount of heatdissipation from each individual optical amplifier.

In accordance with a preferred embodiment of the present invention, theoptical amplification subsystem 106 includes a first plurality ofamplifier assemblies 120, each of which receives an input from a beamsplitter 112. In accordance with a preferred embodiment of the presentinvention, 32 amplifier assemblies are employed, it being appreciatedthat a greater or lesser number may alternatively be employed. Thecomponents specifically described in the illustrated example have beenfound to be suitable for use in an optical amplification subsystem 106including 32 amplifier assemblies.

In accordance with a preferred embodiment of the present invention, eachof the first plurality of amplifier assemblies 120 includes a secondplurality of optical amplifiers and phase control circuitry includingphase modulating functionality associated with each of the secondplurality of optical amplifiers.

As seen in FIG. 1, the second plurality of optical amplifiers which isincluded in each of the first plurality of amplifier assemblies 120includes an optical amplifier 122, preferably a tapered opticalamplifier, which receives one output of beam splitter 112. The output ofoptical amplifier 122 is preferably coupled via a network 124 of opticalfibers to an optical amplification sub-subsystem 126, providing anamplified laser output. Preferably network 124 comprises polarizationmaintaining single mode fibers, such as PM780-HP fibers available fromThorlabs Inc., which are joined via suitable beam splitters.

In a preferred embodiment of the invention, illustrated in FIG. 1,network 124 employs a 1×4 beam splitter 128, such as aPMC-1×N-3-4-2-2-2-0-0 from Micro Optics Inc., which receives the outputof optical amplifier 122 and directs it to four optical amplifiers 130,arranged in parallel. The outputs of each of the four optical amplifiers130 are each directed to a 1×8 beam splitter 132, such as aPMC-1×N-3-8-2-2-2-0-0 from Micro Optics Inc.

In accordance with a preferred embodiment of the present invention, theoptical amplification sub-subsystem 126 includes optical amplifiers 134,each of which receives an input from a beam splitter 132. In accordancewith a preferred embodiment of the present invention, 32 opticalamplifiers 134 are employed, it being appreciated that a greater orlesser number may alternatively be employed. The components specificallydescribed in the illustrated example have been found to be suitable foruse in an optical amplification sub-subsystem 126 including 32 opticalamplifiers 134.

The coherent outputs of the optical amplifiers 134 are coherentlycombined by a coherent combiner 136, preferably of the type describedhereinbelow with reference to FIGS. 4A & 4B. Part of the output ofcoherent combiner 136 is supplied to an intensity sensor 138, such as aPDA10CF from Thorlabs Inc. It is appreciated that output intensity canbe maximized by adjusting the relative phase of the outputs of theindividual optical amplifiers 134. In accordance with a preferredembodiment of the present invention, the output of intensity sensor 138is received by phase control logic circuitry 140, preferably operativein the manner described hereinbelow with reference to FIGS. 2 and 3.

It is a particular feature of the present invention that phase controllogic circuitry 140 is operative to modulate the relative phases of thesecond plurality of optical amplifiers, namely all or most of amplifiers130 and 134, in a manner which maximizes the total output intensity ofthe second plurality of optical amplifiers. Preferably this is achievedby governing the current supplied to optical amplifiers 130 and 134.Alternatively, modulation of the relative phases of the opticalamplifiers may be realized by the use of external phase modulatorsassociated with each of the optical amplifiers. A suitable externalphase modulator may be a LiNbO3 modulator such as a LN65S-SC-10 GHzPhase Modulator, commercially available from Thorlabs Inc. of Newton,N.J. Alternatively phase modulates which are operative by varying thetemperature of the optical amplifier, by mechanically changing thelength of the optical path for each optical amplifier or by employingany other standard phase modulation method may be used.

The remaining coherent outputs of each of coherent combiners 136 arecoherently combined by a coherent combiner 142, preferably of the typedescribed hereinbelow with reference to FIGS. 4A & 4B. Part of theoutput of coherent combiner 142 is supplied to an intensity sensor 144,such as PDA10CF from Thorlabs Inc. In accordance with a preferredembodiment of the present invention, the output of intensity sensor 144is received by phase control logic circuitry 146, preferably operativein the manner described hereinbelow with reference to FIGS. 2 and 3,which governs the current supplied to optical amplifier 122.

It is a particular feature of the present invention that phase controllogic circuitry 146 is operative to modulate the relative phases of thefirst plurality of amplifier assemblies 120, in a manner which maximizesthe total output intensity of the first plurality of amplifierassemblies 120 independently of the operation of phase control logiccircuitry 140.

It is noted that in an example of the embodiment shown above, opticalamplifiers 102, 110, 122, 130 and 134 each having an output of between 1and 10 Watt, which is currently optimal from the standpoint of phasedistortion, wavelength broadening, noise, non-linear effects and heatdissipation are currently employed. It is appreciated that futureoptical amplifiers may have higher outputs which are optimal from thestandpoint of phase distortion, wavelength broadening, noise, non-lineareffects and heat dissipation. Such optical amplifiers, if and whenavailable, may be employed in accordance with an embodiment of thepresent invention.

Thus, using approximate numbers, a 50 mW output of seed laser 100produces 1 Watt at the output of optical amplifier 102; 1 Watt at theoutput of each of the four optical amplifiers 110; 1 Watt at the outputof each of the 32 amplifiers 122; 1 Watt at the output of each of 128amplifiers 130 and 1 watt at the output of each of 1024 amplifiers 134,for a total of 1024 Watt.

It is appreciated the system of FIG. 1 may be scaled up by a furtherfactor of 32 by replacing each of optical amplifiers 134 by an amplifierassembly, such as amplifier assembly 120 which includes 32 opticalamplifiers 134. Further scaling up may be realized in a similar manner.

It is appreciated that from the standpoint of heat dissipation, thesystem of FIG. 1 is highly scalable since the heat sources, e.g. theoptical amplifiers, are distributed throughout the physical volume ofthe system and not concentrated in one location.

It is a particular feature of the present invention that the phasecontrol functionality is highly scalable since it does not become morecomplex as the system is scaled up. Each phase control logic element,such as phase control logic 140 and 146 operates with only a maximum of36 outputs, in the present example, and its operation is not coordinatedwith the operation of another phase control logic element or with anoverall phase control system.

Reference is now made to FIG. 2, which is a simplified diagramillustrating total output intensity based phase modulation, and to FIG.3, which is a simplified flow diagram illustrating the operation of thetotal output intensity based phase modulation of FIG. 2. The descriptionWhich follows is relevant equally to the operation of any and all ofphase control logic elements 140 and 146 (FIG. 1).

Turning initially to FIG. 2, the top trace is the total output intensityas measured by an intensity sensor, such as intensity sensor 138 or 144(FIG. 1). Intensity sensor 138 measures the total output intensity ofeach amplifier assembly 120 (FIG. 1). Intensity sensor 144 measures thetotal output intensity of the laser system including all of theamplifier assemblies 120 taken together.

The second, third, fourth and fifth traces represent the currentsupplied to respective first, second, third and fourth of a plurality ofoptical amplifiers, such as optical amplifiers 130 and 134 (FIG. 1), thecurrent supplied to which governs the output intensity of each amplifierassembly 120 as measured by intensity sensor 138, or such as opticalamplifiers 110 and 122 (FIG. 1), the current supplied to which governsthe output intensity of the laser system including all of the amplifierassemblies 120 taken together, as measured by intensity sensor 144.

As set forth additionally in FIG. 3, referring to the phase controlfunctionality provided by phase control logic 140, it is seen that thecurrent supplied to each optical amplifier is varied, preferably bybeing reduced and thereafter immediately increased linearly in aramp-like fashion. The total output intensity monitored by eachintensity sensor 138 varies non-linearly as a function of the currentsupplied to the optical amplifier and reaches a local peak correspondingto a current level along the current ramp. The current level whichcorresponds to the local peak of total output intensity is set as thecurrent level to that optical amplifier for the meantime.

The above process is repeated for all of the optical amplifiers 130 and134 contributing to the total output which is measured by each intensitysensor 138, sequentially one after the other. Once the process has beencompleted for all of the optical amplifiers contributing to the totaloutput which is measured by each intensity sensor 138, it is repeatedendlessly. It is a particular feature of the present invention thatselection of the input current to each optical amplifier contributing tothe total output which is measured by each intensity sensor 138 takesplace without taking into account the input current supplied to theother optical amplifiers contributing to the total output which ismeasured by that intensity sensor 138.

As set forth additionally in FIG. 3, referring to the phase controlfunctionality provided by phase control logic 146, it is seen that thecurrent supplied to each optical amplifier 110 and 122 is varied,preferably by being reduced and thereafter immediately increasedlinearly in a ramp-like fashion. The total output intensity monitored byintensity sensor 144 varies non-linearly as a function of the currentsupplied to the optical amplifier and reaches a local peak correspondingto a current level along the current ramp. The current level whichcorresponds to the local peak of total output intensity is set as thecurrent level to that optical amplifier for the meantime.

The above process is repeated for all of the optical amplifiers 110 and122 contributing to the total output which is measured by intensitysensor 144, sequentially one after the other. Once the process has beencompleted for all of the optical amplifiers contributing to the totaloutput which is measured by intensity sensor 144, it is repeatedendlessly. It is a particular feature of the present invention thatselection of the input current to each of optical amplifier 110 and 122contributing to the total output which is measured by intensity sensor144 takes place without taking into account the input current suppliedto the other ones of optical amplifiers 110 and 122, contributing to thetotal output which is measured by intensity sensor 144.

It is a particular feature of the present invention that during normaloperation the phase control functionality carried out by phase controllogic 146 can and preferably does take place independently and withoutreference to the phase control functionality carried out by each phasecontrol logic element 140 and further that the phase controlfunctionality carried out by each phase control logic element 140 canand preferably does take place independently and without reference tothe phase control functionality carried out by all other phase controllogic elements 140.

It is appreciated that although in a preferred embodiment of the presentinvention, tapered optical amplifiers are employed, alternatively othersuitable types of optical amplifiers, such as, for example, erbium-dopedfiber amplifiers (EDFA), semiconductor optical amplifiers (SOA) andsolid state optical amplifiers, may be employed.

It is also appreciated that, although in a preferred embodiment of thepresent invention, phase modulation is achieved by varying the currentof the amplifier, other types of phase modulation may be used, such as,for example, using an external phase modulator, such as a LN65S-SC-10GHz Phase Modulator available from Thorlabs Inc. of Newton, N.J.Alternatively, phase modulators which are operative by varying thetemperature of each optical amplifier, by mechanically changing thelength of the optical path for each optical amplifier or by employingany other standard phase modulation method may be used.

Reference is now made to FIG. 4A, which is a simplified illustration ofa coherent optical combiner constructed and operative in accordance witha preferred embodiment of the present invention, useful in the lasersystem of FIGS. 1, 7, 8, 9 and 10. In the context of FIG. 1, forexample, the combiner may serve as combiner 136 or as combiner 142.

As seen in FIG. 4A, a plurality of optical fibers 400, each of whichrepresents the output of an optical amplifier 134, in the case ofcombiner 136, or of amplifier assembly 120, in the case of combiner 142,are preferably arranged in a side by side arrangement along a singleline. A corresponding plurality of collimating lenses 402 are eacharranged to receive substantially the entire light output of acorresponding optical fiber 400.

A preferred construction requires that the light beam output by each ofthe optical fibers 400 cover substantially the entire area of eachcorresponding collimating lens 402. This may be expressed by theconstraint that the numerical aperture of each optical fiber 400,represented by angle alpha (α), is similar to the numerical aperture ofeach corresponding collimating lens 402. Preferably, the numericalaperture of each optical fiber 400 is ±15% the numerical aperture ofeach corresponding collimating lens 402. Most preferably, the numericalaperture of each optical fiber 400 is equal to the numerical aperture ofeach corresponding collimating lens 402.

A plurality of collimated light beams from the plurality of collimatinglenses 402 impinges on a cylindrical focusing lens 404. Cylindricalfocusing lens 404 is arranged to receive substantially the entire lightoutput of all of collimating lenses 402.

Cylindrical focusing lens 404 focuses a beam of light from the pluralityof collimating lenses 402 in the plane of FIG. 4A to a receiving opticalfiber 406. It is a particular feature of the present invention that thebrightness of the coherent beam which is focused on the receivingoptical fiber 406 is substantially higher than the brightness of anon-coherent beam in the same configuration. It is thus appreciatedthat, were a non-coherent beam emitted from the plurality of opticalfibers 400, it would have a much lower brightness than the brightness ofa coherent beam. The numerical aperture of the receiving optical fiber406, represented by the angle beta (β), is similar to the numericalaperture of each optical fiber 400, represented by angle alpha (α).Preferably, the numerical aperture of the receiving optical fiber 406 is±15% the numerical aperture of each optical fiber 400. In the exemplarypreferred embodiment shown in FIG. 4A, the cross sectional area ofreceiving optical fiber 406 is identical to the cross sectional area ofeach of optical fibers 400 and the numerical aperture of the receivingoptical fiber 406, represented by the angle beta (β), is equal to thenumerical aperture of each optical fiber 400, represented by angle alpha(α). It is appreciated that the coherent property of the beam enablessubstantially all of the light output by all of the optical fibers 400to be collected by receiving optical fiber 406.

It is appreciated that focusing of light in a plane orthogonal to theplane of FIG. 4A, to the extent needed, may be provided by a cylindricallens 408. It is also appreciated that if the fibers 400 are arranged ina two dimensional bundle, focusing lens 404 need not necessarily be acylindrical lens and cylindrical lens 408 may be obviated.

In a specific example of the embodiment of FIG. 4A, the followingapproximate parameter values may be employed:

number of optical fibers 400—32

pitch of optical fibers 400—1 mm

number of collimating lenses 402—32

pitch of collimating lenses 402—1 mm

focal length of each of collimating lenses 402—5 mm

focal length f of cylindrical focusing lens 404—160 mm

Reference is now made to FIG. 4B, which is a simplified illustration ofan optical coherent combiner constructed and operative in accordancewith another preferred embodiment of the present invention, useful inthe laser system of FIGS. 1, 7, 8, 9 and 10. In the context of FIG. 1,the combiner may serve as combiner 136 or as combiner 142.

As seen in FIG. 4B, a plurality of optical fibers 420, each of whichrepresents the output of an optical amplifier 134, in the case ofcombiner 136, or of amplifier assembly 120, in the case of combiner 142,are preferably arranged in a side by side arrangement along a singleline. A cylindrical collimating lens 422 collimates the light fromoptical fibers 420 in a direction orthogonal to the plane of FIG. 4B anddirects it to a cylindrical lens 424, having a focal length f, which ispositioned at a distance f from the plurality of optical fibers 420 andreceives substantially the entire total light output of the opticalfibers.

It is a particular feature of this embodiment of the present inventionthat a pair of lens arrays 426 and 428 is positioned at a suitabledistance, such as distance f, from the cylindrical lens 424 and receivessubstantially the entire total light output of lens 424. The lens arrays426 and 428 are identical and are aligned and mutually spaced by adistance g, which is equal to the focal length of each of the lenses inarrays 426 and 428. Lens arrays 426 and 428 together produce a singlebeam of light which impinges on a focusing lens 430.

Focusing lens 430 focuses substantially all of the light output fromlens arrays 426 and 428 onto a receiving optical fiber 432, whichpreferably has a cross sectional area identical to that of each ofoptical fibers 420.

As noted above with reference to the embodiment of FIG. 4A, also in theembodiment of FIG. 4B, it is a particular feature of the presentinvention that the brightness of the coherent beam which is focused onthe receiving optical fiber 432 is substantially higher than thebrightness of a non-coherent beam in the same configuration. It is thusappreciated that, were a non-coherent beam emitted from the plurality ofoptical fibers 420 it would have a much lower brightness than thebrightness of a coherent beam. The numerical aperture of the receivingoptical fiber 432, represented by the angle delta (δ), is similar to thenumerical aperture of each optical fiber 420, represented by angle gamma(γ). Preferably, the numerical aperture of the receiving optical fiber432 is ±15% the numerical aperture of each optical fiber 400. In theexemplary preferred embodiment shown in FIG. 4B, the cross sectionalarea of receiving optical fiber 432 is identical to the cross sectionalarea of each of optical fibers 420 and the numerical aperture of thereceiving optical fiber 432, represented by the angle delta (δ), isequal to the numerical aperture of each optical fiber 420, representedby angle gamma (γ). It is appreciated that the coherent property of thebeam enables substantially all of the light output by all of the opticalfibers 420 to be collected by receiving optical fiber 432.

It is appreciated that focusing of light in a plane orthogonal to theplane of FIG. 4B, to the extent needed, may be provided by a cylindricallens 434. It is also appreciated that if the optical fibers 420 arearranged in a two dimensional bundle, cylindrical lenses 422 and 434 maybe obviated.

In a specific example of the embodiment of FIG. 4B, the followingapproximate parameter values may be employed:

Wavelength—970 nm

number of optical fibers 420—32

pitch of optical fibers 420—250 microns

focal length f of cylindrical lens 424—32.2 mm

minimal number of lenses in each of arrays 426 and 428—42

pitch of lenses in each of arrays 426 and 428—125 microns

focal length g of each of lenses in each of arrays 426 and 428—502microns.

Reference is now made to FIG. 5, which is a simplified illustration of alaser system constructed and operative in accordance with anotherpreferred embodiment of the present invention.

As seen in FIG. 5, there is provided a laser system including a seedlaser 500, typically a 50 MW laser, such as a LU0976M150-1306E10Acommercially available from Lumics Inc. The output of the seed laser 500is amplified by an optical amplifier 502. The output of opticalamplifier 502 is preferably coupled via a network 504 of optical fibersto an optical amplification subsystem, providing an amplified laseroutput. Preferably network 504 comprises polarization maintaining singlemode fibers, such as PM780-HP fibers available from Thorlabs Inc., whichare joined via suitable beam splitters.

In a preferred embodiment of the invention, illustrated in FIG. 5,network 504 employs a 1×4 beam splitter 508, such as aPMC-1×N-3-4-2-2-2-0-0 from Micro Optics Inc., which receives the outputof optical amplifier 502 and directs it to four optical amplifiers 510,arranged in parallel. The outputs of each of the ten optical amplifiers510 are each directed to a 1×8 beam splitter 512, such as aPMC-1×N-3-8-2-2-2-0-0 from Micro Optics Inc.

In accordance with a preferred embodiment of the present invention, thelevel of amplification provided by each of the optical amplifiersemployed in the laser system is significantly below the maximum ratedamplification of the amplifiers and is selected to maximize outputcoherence. More specifically, the level of amplification is selected tolimit the amount of phase distortion and wavelength broadening as wellas to limit noise and non-linear effects produced by the amplifier. Thelevel of amplification is also selected to limit the amount of heatdissipation from each individual optical amplifier.

In accordance with a preferred embodiment of the present invention, theoptical amplification subsystem 506 includes a first plurality ofamplifier assemblies 520, each of which receives an input from a beamsplitter 512. In accordance with a preferred embodiment of the presentinvention, 32 amplifier assemblies 520 are employed, it beingappreciated that a greater or lesser number may alternatively beemployed. The components specifically described in the illustratedexample have been found to be suitable for use in an opticalamplification system 506 including 32 amplifier assemblies 520.

In accordance with a preferred embodiment of the present invention, eachof the first plurality of amplifier assemblies 520 includes a secondplurality of optical amplifiers and phase control circuitry includingphase modulating functionality associated with each of the secondplurality of optical amplifiers.

As seen in FIG. 5, the second plurality of optical amplifiers which isincluded in each of the first plurality of amplifier assemblies 520includes an optical amplifier 522, preferably a tapered opticalamplifier, which receives one output of beam splitter 512. The output ofoptical amplifier 522 is preferably coupled via a network 524 of opticalfibers to an optical amplification and beam combining sub-subsystem 526,providing an amplified laser output. Preferably network 524 comprisespolarization maintaining single mode fibers, such as PM780-HP fibers,available from Thorlabs Inc., which are joined via suitable beamsplitters.

In a preferred embodiment of the invention, illustrated in FIG. 5,network 524 employs a 1×4 beam splitter 528, such asPMC-1×N-3-4-2-2-2-0-0 from Micro Optics Inc., which receives the outputof optical amplifier 522 and directs it to four optical amplifiers 530,arranged in parallel. The outputs of each of the four optical amplifiers530 are each directed to a 1×8 beam splitter 532, such asPMC-1×N-3-8-2-2-2-0-0 from Micro Optics Inc.

In accordance with a preferred embodiment of the present invention, theoptical amplification and beam combining sub-subsystem 526 includesoptical amplifiers 534, each of which receives an input from a beamsplitter 532 via and optical fiber 535. In accordance with a preferredembodiment of the present invention, 32 optical amplifiers 534 areemployed, it being appreciated that a greater or lesser number mayalternatively be employed. The components specifically described in theillustrated example have been found to be suitable for use in an opticalamplification and beam combining sub-subsystem 526 including 32 opticalamplifiers 534, which are coherently combined in free space into asingle output 536. A preferred embodiment of optical amplification andbeam combining sub-subsystem 526 is described hereinbelow with referenceto either of FIGS. 6A & 6B.

Part of the output 536 is supplied to an intensity sensor 538, such asPDA10CF from Thorlabs Inc. It is appreciated that output intensity canbe maximized by adjusting the relative phase of the outputs of theindividual optical amplifiers 534. In accordance with a preferredembodiment of the present invention, the output of intensity sensor 538is received by phase control logic circuitry 540, preferably operativein the manner described hereinabove with reference to FIGS. 2 and 3.

It is a particular feature of the present invention that phase controllogic circuitry 540 is operative to modulate the relative phases of thesecond plurality of optical amplifiers, namely all or most of amplifiers530 and 534, in a manner which maximizes the total output intensity ofthe second plurality of optical amplifiers by governing the currentsupplied to optical amplifiers 530 and 534 or by employing an externalphase modulator associated with each of said amplifiers 530 and 534.

The remaining coherent outputs 536 are coherently combined by a coherentcombiner 542, preferably of the type described hereinbelow withreference to FIGS. 6A & 6B. Part of the output of combiner 542 issupplied to an intensity sensor 544, such as PDA10CF from Thorlabs Inc.In accordance with a preferred embodiment of the present invention, theoutput of intensity sensor 544 is received by phase control logiccircuitry 546, preferably operative in the manner described hereinabovewith reference to FIGS. 2 and 3, which governs the current supplied tooptical amplifier 522 or employs an external phase modulator associatedwith said amplifier 522.

It is a particular feature of the present invention that phase controllogic circuitry 546 is operative to modulate the relative phases of thefirst plurality of amplifier assemblies 520, in a manner which maximizesthe total output intensity of the first plurality of amplifierassemblies 520 independently of the operation of phase control logiccircuitry 540.

It is noted that in an example of the embodiment described herein,optical amplifiers 502, 510, 522, 530 and 534, each having an output ofbetween 1 and 10 Watt, which is currently optimal from the standpoint ofphase distortion, wavelength broadening, noise, non-linear effects andheat dissipation, are currently employed. It is appreciated that futureoptical amplifiers may have higher outputs which are optimal from thestandpoint of phase distortion, wavelength broadening, noise, non-lineareffects and heat dissipation. Such optical amplifiers, if and whenavailable, may be employed in accordance with an embodiment of thepresent invention.

Thus, using approximate numbers, a 50 mW output of seed laser 500produces 1 Watt at the output of optical amplifier 502; 1 Watt at theoutput of each of the four optical amplifiers 510; 1 Watt at the outputof each of the 32 amplifiers 522; 1 Watt at the output of each of 128amplifiers 530 and 1 watt at the output of each of 1024 amplifiers 534,for a total of 1024 Watt.

It is appreciated that the system of FIG. 5 may be scaled up by afurther factor of 32 by replacing each of optical amplifiers 534 by anamplifier assembly, such as amplifier assembly 520 which includes 32optical amplifiers 534. Further scaling up may be realized in a similarmanner.

It is appreciated that from the standpoint of heat dissipation, thesystem of FIG. 5 is highly scalable since the heat sources, e.g. theoptical amplifiers, are distributed throughout the physical volume ofthe system and not concentrated in one location.

It is a particular feature of the present invention that the phasecontrol functionality is highly scalable since it does not become morecomplex as the system is scaled up. Each phase control logic element,such as phase control logic 540 and 546, operates with only a maximum of36 outputs, in the present example, and its operation is not coordinatedwith the operation of another phase control logic element or with anoverall phase control system.

Reference is now made to FIG. 6A, which is a simplified illustration ofan optical amplification and beam combining subsystem constructed andoperative in accordance with a preferred embodiment of the presentinvention, useful in the laser system of FIGS. 5, 7, 8, 9 and 10.

As seen in FIG. 6A, a plurality of optical fibers 535 (FIG. 5), each ofwhich represents the output of a beam splitter 532 (FIG. 5) are coupledto a corresponding plurality of optical amplifiers 534 (FIG. 5), each ofwhich are arranged to receive light output of a corresponding opticalfiber 535. Optical amplifiers 534 are preferably arranged in a side byside arrangement along a single line. A corresponding plurality ofcollimating lenses 602 are each arranged to receive substantially theentire light output of a corresponding optical amplifier 534.

A preferred construction requires that the light beam output by each ofthe optical amplifiers 534 cover substantially the entire area of eachcorresponding collimating lens 602. This may be expressed by theconstraint that the numerical aperture of the output of each of opticalamplifiers 534, represented by angle alpha (α), is equal to thenumerical aperture of each corresponding collimating lens 602. It isappreciated that collimating lens 602 may have a numerical aperture inthe plane of FIG. 6A which is different than the numerical aperture inthe direction with is perpendicular to the plane of FIG. 6A, such aslens 9003-505 from LIMO Lissotschenko Mikrooptik GmbH.

A plurality of collimated light beams from the plurality of collimatinglenses 602 impinges on a cylindrical focusing lens 604. Cylindricalfocusing lens 604 is arranged to receive substantially the entire lightoutput of all of collimating lenses 602.

Cylindrical focusing lens 604 focuses the light from the plurality ofcollimating lenses 602 in the plane of FIG. 6A to a receiving opticalfiber 606. It is a particular feature of the present invention that thebrightness of the coherent beam which is focused on the receivingoptical fiber 606 is substantially higher than the brightness of anon-coherent beam in the same configuration. It is thus appreciatedthat, were a non-coherent beam emitted from the plurality of opticalamplifiers 534, it would have a much lower brightness than thebrightness of a coherent beam. It is appreciated that the coherentproperty of the beam enables substantially all of the light output byall of the optical amplifiers 534 to be collected by receiving opticalfiber 606.

It is appreciated that focusing of light in a plane orthogonal to theplane of FIG. 6A, to the extent needed, may be provided by a cylindricallens 608. It is also appreciated that if the outputs of each of opticalamplifiers 534 are arranged in a two dimensional bundle, focusing lens604 need not necessarily be a cylindrical lens and cylindrical lens 608may be obviated.

In a specific example of the embodiment of FIG. 6A, the followingapproximate parameter values may be employed:

number of optical amplifiers 534—32

pitch of outputs of optical amplifiers 534—1 mm

number of lenses 602—32

pitch of lenses 602—1 mm

focal length of each of lenses 602—5 mm

focal length f of cylindrical focusing lens 604—160 mm

Reference is now made to FIG. 6B, which is a simplified illustration ofan optical amplification and beam combining subsystem constructed andoperative in accordance with another preferred embodiment of the presentinvention, useful in the laser system of FIGS. 5, 7, 8, 9 and 10.

As seen in FIG. 6B, a plurality of optical fibers 535 (FIG. 5), each ofwhich represents the output of a beam splitter 532 (FIG. 5) are coupledto a corresponding plurality of optical amplifiers 534 (FIG. 5), each ofwhich are arranged to receive light output of a corresponding opticalfiber 535. Optical amplifiers 534 are preferably arranged in a side byside arrangement along a single line.

A cylindrical collimating lens 622 collimates the light from the outputsof optical amplifiers 534 in a direction orthogonal to the plane of FIG.6B and directs it to a cylindrical lens 624, having a focal length f,which is positioned at a distance f from the outputs of the opticalamplifiers 534 and receives substantially the entire total light outputthereof.

It is a particular feature of this embodiment of the present inventionthat a pair of lens arrays 626 and 628 is positioned at a suitabledistance, such as distance f, from the cylindrical lens 624 and receivessubstantially the entire total light output of lens 624. The lens arrays626 and 628 are identical and are aligned and mutually spaced by adistance g, which is equal to the focal length of each of the lenses inarrays 626 and 628. Lens arrays 626 and 628 together produce a singlebeam of light which impinges on a focusing lens 630.

Focusing lens 630 focuses substantially all of the light output fromlens arrays 626 and 628 onto a receiving optical fiber 632.

As noted above with reference to the embodiment of FIG. 6A, also in theembodiment of FIG. 6B, it is a particular feature of the presentinvention that the brightness of the coherent beam which is focused onthe receiving optical fiber 632 is substantially higher than thebrightness of a non-coherent beam in the same configuration. It is thusappreciated that, were a non-coherent beam emitted from the plurality ofoptical amplifiers 534 it would have a much lower brightness than thebrightness of a coherent beam. It is appreciated that the coherentproperty of the beam enables substantially all of the light output byall of the optical amplifiers 534 to be collected by receiving opticalfiber 632.

It is appreciated that focusing of light in a plane orthogonal to theplane of FIG. 6B, to the extent needed, may be provided by a cylindricallens 634. It is also appreciated that if the outputs of opticalamplifiers 534 are arranged in a two-dimensional bundle, cylindricallenses 622 and 634 may be obviated.

In a specific example of the embodiment of FIG. 6B, the followingapproximate parameter values may be employed:

Wavelength—970 nm

number of optical amplifiers 534—32

pitch of outputs of optical amplifiers 534—250 microns

focal length f of cylindrical lens 624—32.2 mm

minimal number of lenses in each of arrays 626 and 628—42

pitch of lenses in each of arrays 626 and 628—125 microns

focal length g of each of lenses in each of arrays 626 and 628—502microns

Reference is now made to FIG. 7 which is a simplified illustration of alaser system constructed and operative in accordance with anotherpreferred embodiment of the present invention. FIG. 7 exemplifies afurther scale up of the system of either of FIGS. 1 and 5.

As seen in FIG. 7, there is provided a laser system including a seedlaser 700, typically a 50 MW laser, such as a LU0976M150-1306E10Acommercially available from Lumics Inc. The output of the seed laser 700is amplified by an optical amplifier 702, preferably a tapered opticalamplifier. The output of optical amplifier 702 is preferably coupled viaa network 704 of optical fibers to an optical amplification supersystem706, providing an amplified laser output. Preferably network 704comprises polarization maintaining single mode fibers, such as PM780-HPfibers available from Thorlabs Inc., which are joined via suitable beamsplitters.

In a preferred embodiment of the invention, illustrated in FIG. 7,network 704 employs a 1×8 beam splitter 708, such as aPMC-1×N-3-8-2-2-2-0-0 from Micro Optics Inc., which receives the outputof optical amplifier 702 and directs it to eight optical amplifiers 710,arranged in parallel. The outputs of each of the eight opticalamplifiers 710 are each directed to a 1×8 beam splitter 712, such as aPMC-1×N-3-8-2-2-2-0-0 from Micro Optics Inc.

In accordance with a preferred embodiment of the present invention, theoptical amplification supersystem 706 includes a plurality ofamplification systems 720, each of which typically includes all of theapparatus shown in FIG. 1 downstream of the seed laser 100 or all of theapparatus shown in FIG. 5 downstream of the seed laser 500 (FIG. 5). Theoutputs of combiners 142 (FIG. 1) or combiners 542 (FIG. 5) are suppliedvia optical fibers 722 to respective collimating lenses 724. Opticalfibers 722 are preferably large area mode fibers which can carry lightat a kilowatt power level, commercially available from Nufern, 7 AirportPark Road, East Granby, Conn. 06026. The output ends of optical fibers722 are preferably arranged in a two-dimensional array 726. The separateoutputs of collimating lenses 724, preferably as seen in enlargement A,each propagate and diverge in free space and, at a suitable propagationdistance from lenses 724, combine in a far field pattern, designated byreference numeral 728. A spatial intensity diagram of a near fieldpattern corresponding to the outputs of collimating lenses 724 isdesignated by reference numeral 730. A spatial intensity diagram of thefar field pattern 728 is designated by reference numeral 732. It is seenthat a preferred far field pattern has an intensity profile which is anat least nearly Gaussian profile, as illustrated in diagram 732.

The intensity profile of the far field pattern 728 may be governed bycontrolling the relative phases of amplifiers 102 (FIG. 1) or 502 (FIG.5). This phase control function is preferably achieved by employing acamera 738, which monitors the far field pattern 728. It is appreciatedthat the output intensity of the entire system of FIG. 7 can bemaximized by adjusting the relative phase of the outputs of theindividual optical amplifiers 102 (FIG. 1) or optical amplifiers 502(FIG. 5). In accordance with a preferred embodiment of the presentinvention, the output of camera 738 is received by phase control logiccircuitry 740, preferably operative in the manner described hereinabovewith reference to FIGS. 2 and 3.

Reference is now made to FIG. 8, which is a simplified illustration of alaser system constructed and operative in accordance with anotherpreferred embodiment of the present invention. FIG. 8 exemplifies analternative further scale up of the system of either of FIGS. 1 and 5.

As seen in FIG. 8, there is provided a laser system including a seedlaser 800, typically a 50 MW laser, such as a LU0976M150-1306E10Acommercially available from Lumics Inc. The output of the seed laser 800is amplified by an optical amplifier 802, preferably a tapered opticalamplifier. The output of optical amplifier 802 is preferably coupled viaa network 804 of optical fibers to an optical amplification supersystem806, providing an amplified laser output. Preferably network 804comprises polarization maintaining single mode fibers, such as PM780-HPfibers available from Thorlabs Inc., which are joined via suitable beamsplitters.

In a preferred embodiment of the invention, illustrated in FIG. 8,network 804 employs a 1×8 beam splitter 808, such as aPMC-1×N-3-8-2-2-2-0-0 from Micro Optics Inc., which receives the outputof optical amplifier 802 and directs it to eight optical amplifiers 810,arranged in parallel. The outputs of each of the eight opticalamplifiers 810 are each directed to a 1×8 beam splitter 812, such as aPMC-1×N-3-8-2-2-2-0-0 from Micro Optics Inc.

In accordance with a preferred embodiment of the present invention, theoptical amplification supersystem 806 includes a plurality ofamplification systems 820, each of which typically includes all of theapparatus shown in FIG. 1 downstream of the seed laser 100 or all of theapparatus shown in FIG. 5 downstream of the seed laser 500 (FIG. 5). Theoutputs of combiners 142 (FIG. 1) or combiners 542 (FIG. 5) are suppliedvia optical fibers 822. Optical fibers 822 are preferably large areamode fibers which can carry light at a kilowatt power level,commercially available from Nufern, 7 Airport Park Road, East Granby,Conn. 06026. The output ends of optical fibers 822 are preferablyarranged in a two-dimensional array 826. A lens 828, having a focallength f, is positioned at a distance f from the two dimensional arrayof optical fibers 826 and receives substantially the entire total lightoutput of all of the optical fibers 822.

It is a particular feature of this embodiment of the present inventionthat a pair of lens arrays 830 and 832 each including a multiplicity oflenses of focal length g, is positioned at a suitable distance, such asdistance f, downstream of the lens 828 and receives substantially theentire total light output of lens 828. The lens arrays 830 and 832preferably are identical and are aligned and mutually spaced by distanceg, which is equal to the focal length of each of the lenses in arrays830 and 832. Lens arrays 830 and 832 together produce a single beam oflight which propagates in free space and, at a suitable propagationdistance, produces a far field pattern designated by reference numeral834. A preferred far field pattern is a beam having an at least nearlyGaussian profile as illustrated in an intensity profile of the far fieldpattern, designated by reference numeral 836.

The intensity profile of the far field pattern 834 may be governed bycontrolling the relative phases of amplifiers 102 (FIG. 1) or 502 (FIG.5). This phase control function is preferably achieved by employing acamera 838, which monitors the far field pattern 834. It is appreciatedthat the output intensity of the entire system of FIG. 8 can bemaximized by adjusting the relative phase of the outputs of theindividual optical amplifiers 102 (FIG. 1) or optical amplifiers 502(FIG. 5). In accordance with a preferred embodiment of the presentinvention, the output of camera 838 is received by phase control logiccircuitry 840, preferably operative in the manner described hereinabovewith reference to FIGS. 2 and 3.

Reference is now made to FIG. 9 which is a simplified illustration of alaser system constructed and operative in accordance with anotherpreferred embodiment of the present invention. FIG. 9 exemplifies afurther scale up of the system of either of FIGS. 1 and 5.

As seen in FIG. 9, there is provided a laser system including a seedlaser 900, typically a 50 MW laser, such as a LU0976M150-1306E10Acommercially available from Lumics Inc. The output of the seed laser 900is amplified by an optical amplifier 902, preferably a tapered opticalamplifier. The output of optical amplifier 902 is preferably coupled viaa network 904 of optical fibers to an optical amplification supersystem906, providing an amplified laser output. Preferably network 904comprises polarization maintaining single mode fibers, such as PM780-HPfibers available from Thorlabs Inc., which are joined via suitable beamsplitters.

In a preferred embodiment of the invention, illustrated in FIG. 9,network 904 employs a 1×8 beam splitter 908, such as aPMC-1×N-3-8-2-2-2-0-0 from Micro Optics Inc., which receives the outputof optical amplifier 902 and directs it to eight optical amplifiers 910,arranged in parallel. The outputs of each of the eight opticalamplifiers 910 are each directed to a 1×8 beam splitter 912, such as aPMC-1×N-3-8-2-2-2-0-0 from Micro Optics Inc.

In accordance with a preferred embodiment of the present invention, theoptical amplification supersystem 906 includes a plurality ofamplification systems 920, each of which preferably includes all of theapparatus shown in FIG. 1 downstream of the seed laser 100 or all of theapparatus shown in FIG. 5 downstream of the seed laser 500 (FIG. 5). Theoutputs of combiners 142 (FIG. 1) or combiners 542 (FIG. 5) are suppliedvia collimating lenses 922 and mirrors 924 to preferably form atwo-dimensional array 926. The separate outputs of collimating lenses922 each propagate and diverge in free space and, at a suitablepropagation distance from lenses 922, combine in a far field pattern,designated by reference numeral 928. A spatial intensity diagram of thefar field pattern 928 is designated by reference numeral 932. It is seenthat a preferred far field pattern has an intensity profile having an atleast nearly Gaussian profile, as illustrated in spatial intensitydiagram 932.

The intensity profile of the far field pattern 928 may be governed bycontrolling the relative phases of amplifiers 102 (FIG. 1) or 502 (FIG.5). This phase control function is preferably achieved by employing acamera 938, which monitors the far field pattern 928. It is appreciatedthat the output intensity of the entire system of FIG. 9 can bemaximized by adjusting the relative phase of the outputs of theindividual optical amplifiers 102 (FIG. 1) or optical amplifiers 502(FIG. 5). In accordance with a preferred embodiment of the presentinvention, the output of camera 938 is received by phase control logiccircuitry 940, preferably operative in the manner described hereinabovewith reference to FIGS. 2 and 3.

Reference is now made to FIG. 10, which is a simplified illustration ofa laser system constructed and operative in accordance with anotherpreferred embodiment of the present invention. FIG. 10 exemplifies analternative further scale up of the system of either of FIGS. 1 and 5.

As seen in FIG. 10, there is provided a laser system including a seedlaser 1000, typically a 50 MW laser, such as a LU0976M150-1306E10Acommercially available from Lumics Inc. The output of the seed laser1000 is amplified by an optical amplifier 1002, preferably a taperedoptical amplifier. The output of optical amplifier 1002 is preferablycoupled via a network 1004 of optical fibers to an optical amplificationsupersystem 1006, providing an amplified laser output. Preferablynetwork 1004 comprises polarization maintaining single mode fibers, suchas PM780-HP fibers available from Thorlabs Inc., which are joined viasuitable beam splitters.

In a preferred embodiment of the invention, illustrated in FIG. 10,network 1004 employs a 1×8 beam splitter 1008, such as aPMC-1×N-3-8-2-2-2-0-0 from Micro Optics Inc., which receives the outputof optical amplifier 1002 and directs it to eight optical amplifiers1010, arranged in parallel. The outputs of each of the eight opticalamplifiers 1010 are each directed to a 1×8 beam splitter 1012, such as aPMC-1×N-3-8-2-2-2-0-0 from Micro Optics Inc.

In accordance with a preferred embodiment of the present invention, theoptical amplification supersystem 1006 includes a plurality ofamplification systems 1020, each of which preferably includes all of theapparatus shown in FIG. 1 downstream of the seed laser 100 or all of theapparatus shown in FIG. 5 downstream of the seed laser 500 (FIG. 5). Theoutputs of combiners 142 (FIG. 1) or combiners 542 (FIG. 5) are imagedvia lenses 1022 and mirrors 1024 preferably to form a two-dimensionalarray 1026. A lens 1028, having a focal length f, is positioned at adistance f from the two dimensional array 1026 and receivessubstantially the entire total light output of all of the lenses 1022.

It is a particular feature of this embodiment of the present inventionthat a pair of lens arrays 1030 and 1032 each including a multiplicityof lenses of focal length g, is positioned at a suitable distance, suchas distance f, downstream of the lens 1028 and receives substantiallythe entire total light output of lens 1028. The lens arrays 1030 and1032 preferably are identical and are aligned and mutually spaced bydistance g, which is equal to the focal length of each of the lenses inarrays 1030 and 1032. Lens arrays 1030 and 1032 together produce asingle beam of light which propagates in free space and, at a suitablepropagation distance, produces a far field pattern designated byreference numeral 1034. A preferred far field pattern is a beam havingan at least nearly Gaussian profile, as illustrated in an intensityprofile of the far field pattern, designated by reference numeral 1036.

The intensity profile of the far field pattern 1034 may be governed bycontrolling the relative phases of amplifiers 102 (FIG. 1) or 502 (FIG.5). This phase control function is preferably achieved by employing acamera 1038, which monitors the far field pattern 1034. It isappreciated that the output intensity of the entire system of FIG. 10can be maximized by adjusting the relative phase of the outputs of theindividual optical amplifiers 102 (FIG. 1) or optical amplifiers 502(FIG. 5). In accordance with a preferred embodiment of the presentinvention, the output of camera 1038 is received by phase control logiccircuitry 1040, preferably operative in the manner described hereinabovewith reference to FIGS. 2 and 3.

It is appreciated by persons skilled in the art that the presentinvention is not limited by what has been particularly shown anddescribed hereinabove. Rather the scope of the present inventionincludes both combinations and subcombinations of various featuresdescribed hereinabove as well as variations and modifications theretowhich would occur to a person of skill in the art upon reading the abovedescription and which are not in the prior art.

The invention claimed is:
 1. A laser system comprising: a seed laser;and an optical amplification subsystem, receiving an output of said seedlaser and providing an amplified laser output, said opticalamplification subsystem comprising: a first plurality of more than twoamplifier assemblies, each of said first plurality of more than twoamplifier assemblies including a second plurality of more than twooptical amplifiers arranged in parallel; and first phase controlcircuitry including phase modulating functionality associated with eachof said first plurality of more than two amplifier assemblies, each ofsaid first plurality of more than two amplifier assemblies alsocomprising second phase control circuitry operative to maximize thetotal output intensity of said second plurality of more than two opticalamplifiers.
 2. A laser system according to claim 1 and wherein saidsecond phase control circuitry comprises phase modulating functionalityassociated with each of said second plurality of more than two opticalamplifiers, said second phase control circuitry including a total outputintensity sensor which measures the total output intensity of saidsecond plurality of more than two optical amplifiers and phase controllogic circuitry which receives an output from said total outputintensity sensor and varies the phase relationships of individual onesof said second plurality of more than two optical amplifiers in order tomaximize the total output intensity of said second plurality of morethan two optical amplifiers as sensed by said total output intensitysensor.
 3. A laser system according to claim 2 and wherein said phasecontrol logic circuitry ascertains the current supplied to each of saidsecond plurality of more than two optical amplifiers which produces themaximum total output intensity of said laser system.
 4. A laser systemaccording to claim 2 and wherein said phase control logic circuitrysequentially varies the current supplied to each of said secondplurality of more than two optical amplifiers and selects the currentsupplied to each of said second plurality of more than two opticalamplifiers to be the current which produces the maximum total outputintensity of said laser system.
 5. A laser system according to claim 2and wherein said second phase control circuitry sequentially varies thephase of each of said second plurality of more than two opticalamplifiers and selects the phase of each of said second plurality ofmore than two optical amplifiers to be the phase which produces themaximum total output intensity of said laser system.
 6. A laser systemaccording to claim 5 and wherein multiple different ones of said secondplurality of more than two optical amplifiers are simultaneouslysupplied with different currents.
 7. A laser system according to claim 1and wherein said first phase control circuitry operates independently ofsaid second phase control circuitry.
 8. A laser system according toclaim 1 and wherein said second phase control circuitry of each one ofsaid first plurality of more than two amplifier assemblies operatesindependently of said second phase control circuitry of each other ofsaid first plurality of more than two amplifier assemblies.
 9. A lasersystem according to claim 1 and also comprising a coherent free-spacefar field combiner receiving outputs from at least one of said firstplurality of more than two amplifier assemblies and said secondplurality of more than two optical amplifiers and directing said outputsfrom free-space into a single mode optical fiber.
 10. A laser systemaccording to claim 1 and also comprising a coherent free-space far fieldcombiner receiving outputs having a first numerical aperture from atleast one of said first plurality of more than two amplifier assembliesand said second plurality of more than two optical amplifiers anddirecting said outputs from free-space into an optical fiber having asecond numerical aperture similar to said first numerical aperture. 11.A laser system according to claim 1 and also comprising a coherentfree-space far field combiner receiving outputs from at least one ofsaid first plurality of more than two amplifier assemblies and saidsecond plurality of more than two optical amplifiers and coherentlycombining said outputs from free-space into a single beam having an atleast nearly Gaussian profile.
 12. A laser system according to claim 11and wherein brightness of said single beam is substantially higher thanthe brightness of a corresponding non-coherently combined beam.
 13. Alaser system comprising: a seed laser; and an optical amplificationsubsystem, receiving an output of said seed laser and providing anamplified laser output, said optical amplification subsystem comprising:a plurality of optical amplifiers; and phase control circuitrysequentially varying the phase of each of said plurality of opticalamplifiers and selecting the phase of each of said plurality of opticalamplifiers to be the phase which produces the maximum total outputintensity of said laser system.
 14. A laser system according to claim 13and also comprising a coherent free-space far field combiner receivingoutputs from said plurality of optical amplifiers and directing saidoutputs from free-space into a single mode optical fiber.
 15. A lasersystem according to claim 13 and also comprising a coherent free-spacefar field combiner receiving outputs having a first numerical aperturefrom said plurality of optical amplifiers and directing said outputsfrom free-space into an optical fiber having a second numerical aperturesimilar to said first numerical aperture.
 16. A laser system accordingto claim 13 and also comprising a coherent free-space far field combinerreceiving outputs from said plurality of optical amplifiers andcoherently combining said outputs from free-space into a single beamhaving an at least nearly Gaussian profile.
 17. A laser system accordingto claim 16 and wherein brightness of said single beam is substantiallyhigher than the brightness of a corresponding non-coherently combinedbeam.
 18. A method of independently controlling the phase and outputintensity of an optical amplifier including first and second electrodes,the method including: changing said phase of said optical amplifierindependently of said output intensity of said optical amplifier byvarying current supplied via said first and second electrodes in a firstmanner; and changing said output intensity of said optical amplifierindependently of said phase of said optical amplifier by varying currentsupplied via said first and second electrodes in a second manner,different from said first manner.
 19. A method of independentlycontrolling the phase and output intensity of an optical amplifieraccording to claim 18 and wherein varying current supplied via saidfirst and second electrodes in said first manner includes increasing thecurrent supplied to said first electrode and decreasing the currentsupplied to the second electrode, such that the output intensity of saidoptical amplifier is unchanged.
 20. A method of independentlycontrolling the phase and output intensity of an optical amplifieraccording to claim 18 and wherein varying current supplied via saidfirst and second electrodes in said second manner includes changing thecurrent supplied to said first and second electrodes by differentamounts such that the phase of said optical amplifier is unchanged.